Mocha is a testing framework which is used for writing unit tests for Node Js application. Testing is one of the most important parts of any application development. There are many packages available for implementing testing in a node js application. One of the most common frameworks is Mocha. So, here I am going to show you how you can get started with testing a node js application.

So, let’s start by creating a simple node js application.

Step 1: Start a command prompt and create a new directory: mkdir nodejsapp

Step 2: Navigate to the folder: cd nodejsapp

Step 3: Run the command in command line: node init which creates a package.json file with default settings.

Step 4: Use Command Line to run: npm install mocha –save-dev

Step 5: Copy and paste the below code in your application:

mocha.js

module.exports.add = (x,y) =>{
    return x+y-1;
}

Step 6: Create a folder and create a file inside the folder with name as app.test.js

mocha.test.js

var mochaexample = require('./mochaexample');

it('should be sum of numbers',() => {
    var res = mochaexample.add(2,3);

    if(res !== 5){
      throw new Error(`Result should be 5 but it is ${res}.`); 
    }

    console.log("Test case passed.")

})

Step 7: The final step is to add the mocha code into the script test section:

mocha ***/*.test.js

Once you have added the code into your project you can use the below command to start testing the application:

npm test

Implement Auto Restart using Nodemon

Below is a very simple way which we can use to auto restart our test cases. For achieving this we need to have nodemon package installed globally on our PC. Below is the npm command that can be used to install the nodemon package:

npm install nodemon

After installing the nodemon npm package replace the script for test with the script given below:

 "scripts": {
    "test": "mocha ***/*.test.js",
    "test-watch": "ndeomon --exec \"npm test\""
  }

Now to auto restart the tests you can use the below command:

npm run test-watch

Using Expect with MochaJS

Expect is an npm package that can be used with Mocha for writing the unit test cases in NodeJS. Here I am going to demonstrate how to expect can be used with Mocha for unit testing in the NodeJS application.

First of all you need to install the expect framework using the below command:

npm install --save-dev expect

After installing the package using the npm, you can replace the code as below

require('./mochaexample');

it('should be sum of numbers',() => {
    var res = mochaexample.add(2,3);

    //if(res !== 5){
    //  throw new Error(`Result should be 5 but it is ${res}.`); 
    //}

     expect(res).toBe(5).toBeA('number');

    })